1. Field of the Invention
The invention relates to an expandable medical device, such as a stent, and more particularly, the invention relates to an expandable medical device having hinges or strain concentration features.
2. Description of the Related Art
Permanent and biodegradable stents are used for implantation within a body passageway to maintain patency of the passageway. Coronary stents are typically introduced percutaneously, and transported transluminally until positioned at a desired location. These stents are then expanded either mechanically, such as by the expansion of a balloon positioned inside the device, or expand themselves by releasing stored energy upon actuation within the body. When the stent is permanent and expanded within the lumen, the stent becomes encapsulated within the body tissue and remains a permanent implant. When the stent is biodegradable and expanded within the lumen, the stent becomes encapsulated within the body tissue and degrades over time.
Known stent designs include monofilament wire coil stents (U.S. Pat. No. 4,969,458); welded metal cages (U.S. Pat. Nos. 4,733,665 and 4,776,337); and, most prominently, thin-walled metal cylinders with axial slots formed around the circumference (U.S. Pat. Nos. 4,733,665; 4,739,762; and 4,776,337). Known construction materials for use in stents include polymers, organic fabrics, biocompatible metals, such as stainless steel, gold, silver, tantalum, titanium, and shape memory alloys, such as Nitinol.
Many stents are delivered to an implantation site and deployed by a balloon catheter. Balloon expandable stents are mounted on a balloon at a distal end of a balloon catheter and expanded by inflation of the balloon. However, as the balloon is inflated, often the ends of the balloon and stent will expand first followed by expansion of the center of the balloon and stent. This expansion in a dumbbell shape can result in displacement of the lesion toward the center of the stent.
The stent can also recoil inward after expansion. However, the ends of the stent can recoil further than a center portion due to concentration of the inward forces applied by the vessel walls on the ends of the stent. This can result in an implanted stent with inwardly tapering ends.
Accordingly, it would be desirable to provide an expandable medical device, such as a stent, having improved uniformity during expansion and/or improved uniformity after expansion.